DESCRIPTION: (Applicant's Abstract) The proposed study is designed to broaden the epidemiological and etiological knowledge base on which drug abuse and public health policies rest, and to thereby enhance the efficacy of prevention and treatment efforts regarding the most widely used illicit drug. It proposes to do this by both descriptive and theoretical analyses of marijuana use careers in cities in three different countries. Descriptively, the study will detail the prevalence and patterns of marijuana use in the general population of a high-drug abuse city (San Francisco), and identify the career use patterns and adverse consequences of a representative sample of experienced marijuana users. It will use random, representative household sampling (n=2,100) for a Brief Prevalence Survey using questions from the U.S. National Household Survey on Drug Abuse for comparability. Within this sample, the investigators will conduct an Intensive Interview (2 hours) on a representative sample (n=210) of experienced marijuana users (25 or more lifetime use episodes) on career use patterns, other drug abuse, and a range of adverse health and social consequences. These data will then be analyzed in conjunction with identical data sets, collected via the same sampling procedures and data collection instruments, in Bremen, Germany, and Amsterdam, The Netherlands (this proposal requests funding for only the San Francisco portion of the study). Using this combined data set, the investigators will test a series of hypotheses about the influence of users' psychological sets, social settings of use, and socio-cultural and legal-policy variables on marijuana use patterns, gateway or stepping-stone effects, dependence, and a range of other adverse health and social consequences.